Many systems now use device packages that comprise multiple chips or dies mounted in a single package. Such packages are referred to as system-in-package (SiP) devices. FIG. 1 depicts a conventional arrangement of a SiP package 14. The package 14 comprises two chips 10 and 11. Each die 10, 11 may comprise one or more contacts 16 that connect the die 10, 11 to contacts 17 on the package 14, and then the exterior of the package 14. Each die 10, 11 may comprise one or more die-to-die (D2D) connections 15 that connect the two die 10 and 11 with each other. Each die may have one or more contacts 12 and 13 for the D2D connections 15.
In general, chips are very susceptible to damage or destruction from electrostatic discharge (ESD). ESD occurs when there is a voltage difference between the chip and another object that is brought into contact with the chip. The voltage difference results in a high voltage discharge that damages the circuits on the chip. Since a layer of glass conventionally covers the active areas of the chip, the discharge conventionally enters the chip through the contacts 12, 13, 16.
Consequently, each of the contacts 12, 13, 16 is conventionally protected with one or more ESD protection circuits. Examples of such circuits are shown in FIGS. 2A and 2B.
FIG. 2A depicts a conventional output contact 12 and its related circuitry. Both the contact and its circuitry are located on the die 10. The contact pad 12 is connected to driver 20 that provides the signal that is to be sent out over the contact 12. Paired diodes 21 comprise the ESD circuit that is used to shunt a voltage discharge. For example, the diodes 21 may protect against human body model (HBM) type discharges. HBM type discharges are discharges caused by contact with a human.
FIG. 2B depicts a conventional input contact 13 and its related circuitry. Both the contact 13 and its circuitry are located on the die 11. The contact pad 13 is connected to input receiver 20 that provides the signal that is to be used inside of die 11. Paired diodes 21 and 23 comprise the primary ESD circuits that are used to shunt a voltage discharge. For example, diodes 21 may protect against primary discharge events, such as human body model (HBM) type discharges. Furthermore, diodes 23 serve as secondary protection circuitry, and may protect against secondary discharge events, such as charge device model (CDM) type discharges. CDM type discharges result from contact with another electronic device. Note that the resistor 22 is part of the secondary protection circuitry and limits current.